The present invention relates to an extrusion forming apparatus having clamping means in a simple structure.
Extruders for extruding rubber or other plastic materials and producing various formings such as sheets and pipes are widely used. In such extruders, for exchanging the nozzles to clean the passage of the plastic materials or changing the shape of extrusion, a movable head is disposed in the head main body part contiguous to the extruder main body, so that the head main body part and the movable head may be separated.
However, since a passage is formed between the head main body part and movable head, and a plastic material of high pressure passes through this passage, a strong separating force acts, and it is necessary to clamp the two very firmly.
In particular, as schematically shown in FIG. 1, where plural extruder main bodies 5A, 5B are provided, movable heads 7, 7 are attached to the upper and lower part of the head main body part 6, and the separating force is large, and hence it is required to seal the joint surfaces by firm clamping.
For such clamping, hitherto, a powerful hydraulic cylinder was used, or a toggle mechanism was employed.
Where a hydraulic cylinder is used, if a boosting mechanism is combined, the size of the hydraulic cylinder becomes large, and a hydraulic cylinder is needed on every movable head, thus the apparatus cost increases and the maintainability is impaired. On the other hand, where the toggle mechanism is used, the construction is complicated, and high precision linking is needed, and the manufacturing cost soars.